R1

R2

R3

V1

V2

V3

RF

VOUT

VREF

-

+

Copyright © 2016, Texas Instruments Incorporated

VOUT = RF ¨

¨

©

§ V

REF - V1

R1

+

VREF - V2

R2

+

VREF - V3

R3

+ VREF

0

1

2

3

4

5

0

1

2

3

4

5

ICHARGE (A)

C001

17

LPV511

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SNOSAG7D – AUGUST 2005 – REVISED AUGUST 2016

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Typical Applications (continued)

IG also flows through the gain resistor R3 developing a voltage drop equal to:

V3 = IG × R3 = ( VRSENSE / R1 ) × R3 = ( ( RSENSE × ICHARGE ) / R2 ) × R3

(2)

VOUT = (RSENSE × ICHARGE ) × G

where

•

G = R3 / R1

(3)

8.2.1.3 Application Curve

Figure 29 shows the results of the example current sense circuit.

The error after 4 V where transistor Q1 runs out of headroom and saturates, limiting the upper output swing.

Figure 29. Current Sense Amplifier Results

8.2.2 Summing Amplifier

The LPV511 operational amplifier is a perfect fit in a summing amplifier circuit because of the rail-to-rail input and

output and the sub-micro Amp quiescent current. In this configuration, the amplifier outputs the sum of the three

input voltages.

Equation 4 shows the ratio of the sum and the output voltage is defined using feedback and input resistors.

(4)

Figure 30. Summing Amplifier Circuit

8.3 Dos and Don'ts

Do properly bypass the power supplies.

Do add series resistence to the output when driving capacitive loads, particularly cables, Muxes and ADC inputs.

Do add series current limiting resistors and external Schottky clamp diodes if input voltage is expected to exceed

the supplies. Limit the current to 1 mA or less (1 kΩ per volt).